High-amplitude ferromagnetic soft mode at the spin-reorientation transition in an iron garnet film excited by ultrashort laser pulses
Phys. Rev. B 111, 224424 – Published 23 June, 2025
DOI: https://doi.org/10.1103/czrs-yvwx
Abstract
Magnetic materials are promising for the ultrafast and Joule-loss free data storage and processing devices, where the information is encoded by a spin state. Femtosecond pulses are known as an efficient method of spin control with such advantages as ultrafast subpicosecond timescales, submicron spatial localization, and tunability as well. At the same time, quite low amplitude of optically launched spin dynamics is a stumbling block for optomagnetic applications. We propose a way to increase efficiency of photon-spin interaction and to launch large-amplitude spin precession nonthermally by optical pulses in the special types of the ferrimagnets. The key point is to use a soft mode excited in a low damping ferrimagnetic film near the spin-reorientation phase transition between the collinear and noncollinear phases. The physical mechanism of the enhanced spin dynamics is in a dramatic growth of the spin susceptibility to the nonthermal impact of the circularly polarized femtosecond laser pulses which takes place at the phase transition. The observed dynamic deviation of spins from their equilibrium position reaches 9 ° for an optical pump fluence of which is significantly higher than typical values of optically induced precession reported before.
